1. Field of the Invention
The present invention generally relates to semiconductor devices and methods of producing the same, and more particularly to a multi-chip module in which a plurality of semiconductor chips are mounted on the upper major surface of a wiring circuit board, and to a method of producing the same. A more specific application of the present invention is to a multi-chip module in which a plurality of semiconductor chips are mounted both on the upper major surface of a wiring circuit board and on the lower major surface thereof, and to a method of producing the same. The present invention concerns the radiating structure of a multi-chip module (multi-chip semiconductor device).
Recently, there has been a demand for rapid signal processing in the field of computer technology. In order to meet this demand, a method by which a multi-chip module is produced and mounted on a mounting base board (motherboard) is employed. A multi-chip module is a module in which a plurality of related semiconductor chips constituting a system, instead of a single semiconductor chip, are mounted on a thin-film multi-layer wiring circuit board.
As individual semiconductor chips become highly integrated, the power consumption and the amount of heat radiated from individual chips tends to increase.
Hence, a semiconductor device having a structure capable of radiating heat efficiently is demanded.
2. Description of the Related Art
Generally, the great capability of a semiconductor device called a multi-chip module is derived from its construction in which a plurality of semiconductor chips are mounted on a single circuit board. Conventionally, in such a semiconductor device, the wiring circuit board and the semiconductor chips are not hermetically sealed in a package. The heat generated by the semiconductor chips is wasted in the environment by radiation or transferred via a gap between the circuit board and a cap adhesively attached to the circuit board to cover the semiconductor chips.
Recently, semiconductor devices having radiating fins adhesively attached to the upper major surface of a cap have been provided. In such semiconductor devices, the heat transferred to the cap through the gap is radiated using the radiating fins. Conventionally, the radiating fins are fixed to the upper major surface of the cap by an adhesive.
One example of the related art is a multi-chip module 10 shown in FIG. 1. The multi-chip module 10 is disclosed in the Japanese Patent Application No. 5-205444 filed by the applicants of the present invention.
The multi-chip module 10 includes a thin-film multi-layer circuit board 311, semiconductor chips 312.sub.-1 and 312.sub.-2, heat conductive blocks 313.sub.-1 and 313.sub.-2, a resin package 314, a heat sink 315 and leads 316.
As indicated by arrows 317, the heat generated by the semiconductor chips 312.sub.-1 and 312.sub.-2 is transferred to the heat sink 315 via the heat conductive blocks 313.sub.-1 and 313.sub.-2. The heat is then radiated to the surrounding atmosphere from the heat sink 315.
The thin-film multi-layer circuit board 311 comprises a ceramic circuit board 318 formed of Al.sub.2 O.sub.3 and a thin-film multi-layer wiring layer 319 provided on the ceramic circuit board 318.
A semiconductor device configured to have radiating fins adhesively attached to the upper major surface of the cap is heat-treated in order to harden the adhesive used to attach the radiating fins. As a consequence of this heat treatment, a thermal stress at a joint between the wiring circuit board and the semiconductor chips is generated. The residual thermal stress may create a crack in the wiring circuit board or the semiconductor chips.
Further, even in the structure in which the heat radiating fins are employed, a gap formed between the cap and the circuit board serves as a heat transfer passage. Hence, an inefficient heat radiating efficiency results.
In the conventional semiconductor device, the cap is fixed to the wiring circuit board by an adhesive or attached to a base member provided underneath the wiring circuit board. This arrangement has a disadvantage in that it is impossible to remove a cap once it is fixed in place adhesively. Therefore, the problem of poor maintainability is encountered when, for example, any of the semiconductor chips fails.
In order to increase the density with which the semiconductor chips are mounted, a thin-film multi-layer circuit board of a multi-chip module may be configured such that the thin-film wiring layer is provided on the lower major surface of a ceramic circuit board as well as on the upper major surface thereof so that the semiconductor chips are mounted on the underside of the thin-film multi-layer circuit board as well as on the topside thereof.
However, the semiconductor device having the above construction has a disadvantage in that the heat generated by the semiconductor chips mounted on the underside of the thin-film circuit board is not radiated efficiently.